1. Field of the Invention
The invention concerns a device for transmitting ultrasonic energy to a liquid or pasty medium. A device of this type is the subject matter of a co-owned, not published patent application (DE 195 39 195 A1).
2. Description of the Related Act
In the known devices in this technology (U.S. Pat. No. 4,016,436) there is provided on one side of a tubular shaped hollow chamber resonator a waveguide, which by means of a piezoelectric transducer, which for its part converts electrical alternating current voltage (a.c. voltage, hereafter alternating current) output signals of an alternating current generator into longitudinal mechanical oscillations, is excitable to resonant longitudinal oscillations. Onto this transducer, a hollow chamber resonator is mechanically rigidly acoustically coupled in a flange-shaped area of the transducer.
In a further device of similar type (U.S. Pat. No. 5,200,666), ultrasonic energy is transmitted on both ends of the tubular shaped resonator, which is provided for conversion of longitudinal oscillations into transverse oscillations, by means of respectively one transducer.
It is also known (U.S. Pat. No. 4,537,511) to employ a tubular shaped hollow chamber resonator, which is closed on both ends and from one side is acted upon by ultrasound transmitted by a transducer.
In all of these devices, the length of the hollow chamber resonator is selected similarly in a first approximation according to the equation
L=nc0/2frxe2x80x83xe2x80x83(A)
in which n represents a whole number, c0 represents the sound velocity in the rod shaped resonator, and fr represents the mechanical resonance frequency of the waveguide employed for introduction of ultrasound into the resonator and acoustically coupled with a transducer. The sound velocity c0, is provided by the equation
c0={square root over (E+L /xcfx81)}xe2x80x83xe2x80x83(B)
in which E represents the modulus of elasticity (Young""s Modulus) and xcfx81 represents the specific weight of the resonator material.
In so far as sub-optimal results are achieved by the selection of the resonator length according to the first mentioned equation (A), it is conventional to use experimental attempts to determine the correction of the resonator length, which process, however, is only rational or justifiable, when subsequently a larger number of such devices are to be constructed with this optimized length as determined by experimental attempts. Special devices, which are only constructed in small quantities, are thus very expensive. In addition to this, it may occur that during such a process the result is often times relatively far from the theoretical optimum, which is however taken into consideration, since the device can be suitably produced for the intended purpose by employment of a high output frequency generator and transducer. However, these devices are expensive as a result of the necessity of over-dimensioning their electronic supply and transducer.
It is thus the object of this invention, to provide a design for the above-mentioned device, which produces an economically high transmission efficiency and, after which it has once been designed, there is no, or at least no significant, requirement for follow-up processing in order to arrive at dimensions for an operation with optimal working efficiency, in particular, a device having a pre-determined design which operates with a working efficiency which is close to the optimal working efficiency.
The deviation of the resonator length from the relation (A) could be relatively small, so that the inventive arrangement with respect to the equation (A) produces only a correspondingly minimal improvement, but it could however in practical cases also deviate by almost 40% from the result obtainable by the equation (A), so that, compared with such a case, the inventive design or arrangement provides a substantially improved result.
Also, for the closed design of the hollow chamber resonator, by the inventive arrangement of its length L, its outer diameter D, and its wall thickness a very precise tuning to the resonance requirements can be achieved. In the closed configuration of the hollow chamber resonator, this can be flushed with a liquid cooling medium and can be advantageously employed in this case for ultrasonic treatment of molten metals, in order to achieve a high as possible fineness and homogeneity of the grain size in the cooled, xe2x80x9chardenedxe2x80x9d, condition of the treated material.
There can be achieved in particular for the ultrasonic treatment of fluids an advantageous intensification of the cavitation bubble formation in the material being treated.
The design of the device provides the advantage of a substantially homogenous distribution of the ultrasonic energy radiated into the material being treated.
In the design of the resonator of the inventive device, there is a transport effect along the resonator faults, which leads to the result of a more even or homogenous treatment of the xe2x80x9cflowingxe2x80x9d material.
By the xe2x80x9ceccentricxe2x80x9d arrangement of the resonator inner chamber as opposed to the central longitudinal access of its outer jacket surface, there is achieved a directionality effect with respect to the radiated ultrasonic field of such a type, that more ultrasound energy is radiated through the thinner walled area of the resonator jacket than through the thicker walled jacket area. The device following the basic concept of the invention and in certain cases embodiments comprised of multiple hollow chamber resonators, overall longitudinally extending rod shaped ultrasound source has the advantage of its space-saving arrangement of the transducer within the resonator elements and offers also the possibility of radiating particularly high sound capacities into the material being treated. In combination herewith, it is advantageous or useful to employ alternating current controlled transducers as the voltage-sound converter and therein to control or drive the transducers adjacent to each other in the longitudinal direction of the ultrasound source counter-phasic or in phase opposition.